1. Field of the Invention
This invention relates to a tape guide roller for a tape cassette, which is disposed within a tape cassette and is used to guide the running of a magnetic tape accommodated within the tape cassette.
2. Background
Generally, tape cassettes of the structure shown in FIG. 1 include a pair of tape reels 2 and 3 which are rotatably accommodated within a cassette 1, comprised of an upper half la and a lower half 1b combined by butt joining and having a magnetic tape 4 wound between the tape reels 2 and 3.
Within the cassette 1, in order to guide the direction of movement of the magnetic tape 4 as it travels between the pair of tape reels 2, 3, tape guides 5a, 5b and 5c and a plurality of tape guide rollers 6 (only one is shown in the figure) are disposed. One tape guide 5a is disposed in such a manner that it projects upwardly from the lower half lb at a position in the vicinity of the tape reel 3. The tape guides 5b and 5c are located at positions in the vicinity of window portions 7, 7 for directing the magnetic tape 4 as it extends across the front side of the cassette 1. In addition, the tape guide roller 6 is disposed between the tape guide 5c and the tape reel 2. During operation, the tape guide roller 6 functions to direct the magnetic tape 4 into a position so that when the tape cassette is loaded into, e.g., a video tape recorder, the tape guide roller 6 rotates, following the running of the magnetic tape 4 and smoothly guides the running direction of the magnetic tape 4.
It is noted that while the tape guide roller 6 is disposed between the tape reel 2 and the tape guide 5c in the example shown in FIG. 1, similar tape guide roller 6 may be disposed between the tape reel 3 and the tape guide 5b and between the tape reel 2 and the tape guide 5c. In such a case, the tape guide 5a disposed on the tape reel 3 side becomes unnecessary.
For conventional tape cassettes, tape guide rollers formed by cutting or machining a synthetic resin body so that they take a cylindrical form, are widely used. Such tape guide rollers are used to guarantee sufficient circularity, to guarantee that the tape guide roller 6 can smoothly rotate without producing rotation noise, etc. when attached on a support shaft 8 projecting upwardly within the cassette half lb as shown in FIG. 2, and to guarantee precise guidance of the magnetic tape 4.
However, although it is possible using tape guide rollers formed by cutting a synthetic resin body as described above to guarantee sufficient machining accuracy, there is the problem in that the machining efficiency is extremely poor, so the productivity is extremely poor.
In view of this, and in order to eliminate problems with tape guide rollers formed by machining, such as cutting, and to attain improvements in the machining efficiency and productivity, tape guide rollers formed by a molded body of synthetic resin (plastic) are used.
Meanwhile, it is necessary that the tape guide rollers disposed within the tape cassette have sufficient strength so that they can tolerate repetitive use. In addition, it is necessary that the tape guide rollers rotate in a stable manner without producing deformation, etc. when it runs with a magnetic tape being wound thereon, i.e., while it serves to guide the running of the magnetic tape.
In order to satisfy these requirements, a tape guide roller 9 (FIG. 3) comprised of synthetic resin formed as a single cylindrical body having sufficient thickness has been used. In such a tape guide roller 9, however, when molten synthetic resin material is molded by a metal mold unit and the molded material is then cooled, there occurs a so-called sink or withdrawal wherein portions of the roller circumference, in the vicinity of the central portions of the outer circumferential surface 9a and the inner circumferential surface 9b, are caused to be thinner in thickness as shown in FIG. 3, thus failing to maintain straightness and circularity, etc. As a result, when such a tape guide roller 9 is attached on a support shaft 8 within the cassette, it does not rotate coaxially with the support shaft 8 without any eccentric rotation. Thus, rubbing between the tape guide roller 9 and the internal surface of the cassette 1, or the like takes place, giving rise to rotation noise. In addition, since the outer circumferential surface 9a, which serves as the guide surface for the magnetic tape 4, is curved it becomes impossible to guide the magnetic tape 4 in a stable manner and in a direction corresponding to the running direction.
In order to solve the problems with such tape guide rollers, i.e., those formed as a single cylindrical body having sufficient thickness, a tape guide roller as described in the Japanese Patent Application Laid Open No. 24926/1991 publication has been proposed.
The tape guide roller described in this publication has a double layer structure comprised of a cylindrical body on the inner circumferential side and a cylindrical body on the outer circumferential side, and is formed by molding these cylindrical bodies by using a double molding machine. More particularly, the cylindrical body on the inner circumferential side of the tape guide roller is molded using a double molding machine. It comprises a cylindrical body having the same diameter from one end side to the other side, or a cylindrical body formed so that a projection of a small diameter is projected on one end surface at one end side thereof. Since the cylindrical body on the inner circumferential side is molded with the end surface on one end side thereof being caused to be a gate portion serving as an injection portion for synthetic resin (plastic) material, the diameter of the portion on the other side opposite to the gate portion is contracted. Particularly, where the cylindrical body on the outer circumferential side is molded on a double molding machine, the inner circumferential side undergoes contraction relative to the outer circumferential side, so the end side opposite to the gate portion is contracted to a considerable extent.
As a result, it become impossible to guarantee sufficient circularity of a tape guide roller formed by molding.
In addition, a tape guide roller disposed within a tape cassette used in a video tape recorder for business use may rotate at an extremely high speed of 15,000 rpm at the time of running of a magnetic tape, while a tape guide roller disposed within a tape cassette for consumer use may rotate at a rotational speed of 3,000 to 4,000 rpm. For the above reasons, in tape guide rollers designed to rotate at an extremely high speed, straightness and circularity of extremely high accuracy is required.